1. Field of the Invention
The present invention relates to a bodily sensed vibration generator system mountable on small-sized information terminal devices, such as portable telephones, PDA, portable game equipments, and so on, and more particular, to a bodily sensed vibration generator system, which is small in size and capable of realizing a variety of vibrations.
2. Description of Related Art
For example, Patent document 1 discloses an invention of a conventional vibration generator system.
The vibration generator system may be used as a drive device for speakers, and in which a cylindrical-shaped coil is fixed on a side of a bottom surface of a housing and a magnetic field generator composed of a magnet and a yoke is elastically supported in a position opposed to an outer surface of the coil by a plate-shaped elastic body or a coil spring. When a drive signal is given to the coil, an electromagnetic force acts between the magnetic field generator and the coil to vibrate the magnetic field generator.
Also, a column of the prior art in Patent document 1 describes a biased weight type vibration generator system as a general vibration generator system. With the biased weight type vibration generator system, a biased weight having a non-axisymmetric shape is provided on a tip end of a rotating shaft of a motor and vibrations are generated by making a center of gravity of the biased weight offset from a center of rotation when the rotating shaft is rotated.
[Patent Document 1]
JP-A-9-205763
However, the vibration generator system described in Patent document 1 is directed to bodily sensing vibrations when the magnetic field generator generates natural vibrations. However, the number of vibrations that can be bodily sensed by humans is in a relatively low frequency band. The natural frequency of mechanical vibration is inversely proportional to the square root of a mass of a movable part and proportional to the square root of a spring constant. Accordingly, in order to generate natural vibrations at that frequency, which can be bodily sensed by humans, the movable part must have a considerably large mass since the movable part is limited in stroke. A drive part must have a large volume correspondingly, so that in order to generate natural vibrations of that amplitude, which can be bodily sensed by humans, equipments is large.
Also, while an increase in frequency of natural vibrations is conceivable for the sake of miniaturization, it is also difficult since the number of vibrations that can be bodily sensed by humans is in a relatively low frequency band.
Also, while the vibration generator system can generate simple vibrations based on the frequency of natural vibrations continuously or intermittently, it is not possible to freely set a configuration of vibrations. Accordingly, it is not possible to mount the system on portable telephones or portable game equipments to generate a variety of effective vibrations.
Meanwhile, the conventional biased weight type vibration generator system is constructed to have a motor and a biased weight and so becomes large-sized, and it becomes necessary to firmly fix the motor in a manner to withstand vibrations caused by rotation of the biased weight, so that miniaturization of the system is impeded. Also, since a large inertial force acts on the biased weight in rotation, it is hard to finely vary intensity (mode of vibration) of vibrations by giving various drive signals and modifying the rotating speed. That is, the biased weight type vibration generator system involves a problem of a poor follow-up property of the vibration system for drive signals.